1. Field of the Invention
The present invention relates to the field of composite materials, and more specifically composite laminates made of fibers that are organized or not organized as fabrics or plies and fixed in matrices made of polymer resin.
More specifically, the invention relates to a composite laminate in the form of a thin sheet, which can be used to manufacture sports articles such as sports boots (bottom assembly, vamp/upper), roller skates, skis, snowboards, skate-boards, golf clubs, scooters, cycles (frames, wheels), fishing rods, racquets, cross-country ski poles, backpack frames, tent pegs, for example.
2. Description of Background and Relevant Information
Composite materials are materials which have a thermohardening or thermoplastic polymer matrix and a fibrous reinforcement, and possibly granular fillers and additives. The polymer matrix plays the role of a binder for the fibers of the reinforcement. It distributes and ensures the transmission of the forces to the fibers. The fibrous reinforcement, oriented (woven or non-woven) or random (non-woven) provides the finished composite with the mechanical strength and rigidity properties. These composites are used as raw material in the automotive industry, shipyards, aircraft industry, textile industry, sports article industry (boots, skis, golf clubs . . . ). 65% of the manufactured composites are glass fiber-reinforced polyester or vinylester resins manufactured according to the open molding technique. The remaining 35% are formed by special resins (phenolic resin, polyurethane resin, and silicone resin), reinforced by carbon or aramide fibers.
The composites can be in the form of sandwich or laminated constructions, formed by a plurality of superimposed fibrous layers embedded in the matrix. In these composite laminates (or sandwiches), one distinguishes a central structure, also called composite core or central member, linked through each of its surfaces to an external composite layer. These sandwich or laminated composite constructions have the characteristic of being relatively lightweight and extremely rigid. This stiffness is such that deformability is very reduced. It is then easily understood that such mechanical properties render difficult the working and shaping of the pieces obtained in composite laminates.
U.S. Pat. No. 3,873,168 describes an article made of composite laminate having a body 14 constituted by a polyamide cross-linkable resin and reinforced by a glass fiber. This body is inserted between two composite outer bearing portions whose matrix is also made of cross-linkable polyamide resin, and whose fibrous reinforcement is formed by a graphite fiber. The composite laminate according to U.S. Pat. No. 3,873,168 has the disadvantage of being too rigid and relatively expensive. Indeed, the fibers used are high performance, therefore costly fibers or fiber fabrics.
U.S. Pat. No. 3,779,851 discloses a composite laminate constituted of a plurality of graphite fiber sheets impregnated with epoxide resin. This laminate is presented as having a very high mechanical strength to weight ratio, as well as very low thermal expansion properties. Such specifications are desired for applications of these composite laminates in the manufacture of optical instruments (mirror). These are also extremely rigid composite laminates. The total thickness of the composite laminates according to U.S. Pat. No. 3,779,851 is 3.6 mm, for example, even 3 mm as a minimum (12 inches×0.254). The sheets used to manufacture this laminate are sheets preimpregnated with carbon fibers in an epoxy resin matrix. This composite laminate has a too substantial stiffness to be used as raw material in the manufacture of sports articles, such as boots, for example, where a certain deformability or bending ability in the longitudinal direction is needed. In addition, the fibrous reinforcement is exclusively made of carbon fibers. This results in a prohibitive cost for fields of application such as that of sports articles, which are produced at large scale and at very low cost, contrary to what can be found in frontier technological fields, such as aeronautics or aerospace.
Furthermore, it is known to use shock absorbing means constituted by laminated structures including composites in sports articles, in particular gliding members, such as skis, ice-skates, roller skates, snowboards.
Thus, the French Patent Application No. 2 742 063 discloses a roller skate chassis having a shock absorbing means, constituted by a laminate including, successively, a rigid stress layer and a viscoelastic layer. The laminate can include one or several pairs of rigid layer/viscoelastic layer. The rigid layer is made of a plastic material having a high modulus of elasticity, from composite fibers or from aluminum, these materials being selected for their rigidity or their lightweight. The viscoelastic layer is made of rubber or of synthetic elastomer. To obtain the desired shock absorbing effect, the composite-rubber laminate according to FR 2 742 063 necessarily has a thickness greater than or equal to 3 mm. Moreover, this composite laminated shock absorbing means remains perfectible in terms of deformability, cost, and weight gain.
The French Patent Application Publication No. 2 730 416 describes a golf club shaft constituted by a laminate having a composite outer layer made of resin reinforced with:                carbon fibers, a central core (or central member) made of polymer foam, synthetic or natural resin, cork, wood or the like; and        an inner composite layer made of glass fiber-reinforced resin.The density of the composite inner and outer layers is greater than 1.2 kg/dm3 and their longitudinal Young's modulus E1 is greater than 20 Gpa. The polymer foam core has a density lower than 1.2 kg/dm3 and a longitudinal Young's modulus E3 lower than 20 Gpa. This composite laminate has a thickness between 0.2 and 9 mm. Here again, it has been found that the stiffness/deformability/durability/weight gain compromise is not entirely satisfactory for this composite/polymer foam/composite laminate according to this French Patent Application Publication No. 2 730 416.        
This review of the state of the art shows that the manufacturers of sports articles are always looking for a raw material having the mechanical properties of the composites in terms of maximum stiffness and minimum deformability, combined with a vibration dampening capacity, which is inexpensive and lightweight. These manufacturers also expect such a raw material to be easily industrially workable and shapable and, finally, to preserve its mechanical properties over a long period of time.